1. The effect of refractive index (R.I.) of the solution on the fluorescence signal in a spectrofluorometer was analyzed theoretically and experimentally. Although texts state that signal should be proportional to the square of R.I., this was shown to apply only in special cases; in available fluorometers, it is best not to apply correction factor for R.I.'s from 1.3 to 1.6. 2. The fluorometric method for detecting surface-active peptides has been extended to the assay of antibiotics such as gramicidin and polymyxin - indeed to many membrane channel-formers. The method uses liposomes which lyse in the presence of certain peptides, releasing entrapped fluorescent dye. 3. The precision of the steady-state fluorescence depolarization method for analyzing protein relaxation rates depends on photometric precision, the fluroescence lifetime, and the limiting polarization. An expression relating experimental precision to these factors was derived and tested. 4. Storage and analysis of data from a photon counting decay time apparatus has been achieved with an inexpensive microcomputer.